Single-ply roofing (SPR) membrane made from ethylenepropylene-non-conjugated diene rubbery terpolymer (EPDM) is manufactured in large sheets. These sheets can be from 7 to 40 or more feet wide and 100 or more feet long. During installation, these sheets must be connected at their edges into a watertight seam.
Traditionally, the seams for EPDM SPR are made using a polychloroprene contact adhesive in a simple lap seam. The area to be overlapped, 2 or 3 inches, is washed usually with a solvent such as white gas. Then the contact adhesive is applied to both surfaces before the seam is formed. After the seam bond is formed, a "lap sealant" is applied to the overlapped edge. This "lap sealant" protects the adhesive from oxygen, ozone, ultraviolet radiation, water and other elements.
Seaming SPR membrane by the above method has disadvantages. The solvent is flammable and its fumes are obnoxious. If the lap sealant is torn away exposing the adhesive, the seam is likely to leak eventually.
In addition to these problems of installation, the peel strength of the contact adhesive which is normally used is considered low. It is usually only about 2 pli (pounds per linear inch) at RT and 1.5 pli at 158.degree. F.
Because of the problems of installation and the inherently low peel strength achieved with polychloroprene adhesives, alternative adhesive methods have been sought. One of these is the use of seaming tapes. Seaming tapes are sticky strips of caulk-like adhesive usually 2-3 inches wide and nominally 0.040 inch thick. They are placed between the overlapped layers of the roofing membranes. Two general types have been introduced or experimented with: non-curable and roof-curable.
Non-curable tapes contain no cure system. They are manufactured, shipped, installed and remain in service indefinitely in the uncured state. Roof-curable tapes contain a curative system, but are not intended to crosslink until after installation.
Both types of tape (non-curable and roof-curable) have advantages, but also disadvantages.
Non-curable tapes are easy to manufacture, ship, store and install because there is no worry about precuring (scorch) before installation. However, since they never cure, even after installation, peel strength never increases with time. Therefore, peel strength, especially at temperatures of 160.degree.-180.degree. F. (realistic roof-top temperatures) is usually extremely low, in the range of 0.5 pli or less.
Roof-curable tapes must be carefully manufactured, shipped, stored and installed to insure that they do not cure before installation. Precure can make a roof-curable tape less sticky than desired, even to the point of being nonserviceable. It is difficult to avoid precure, especially since the tape is designed to cure at ambient roof-top temperatures in a reasonably short period of time. This requires a low temperature cure system, which greatly aggravates the problems of precure or scorch. Even if properly installed, roof-curable tape has low initial peel strength, no better than non-curable tapes. This could be a problem, particularly for hot-weather installations. During hot weather, roof-top temperatures can reach 160.degree.-180.degree. F. At these temperatures, the initial peel strength of the uncured roof-curable tape can easily be 0.5 pli or less.
An object of the present invention is to provide a laminate of two EPDM roofing membranes joined at their seams with a seaming tape which overcomes the above difficulties.